Met enkephalin is an opiate-like compound found in brain and in gut. Since gut survives well in vitro, we chose this tissue to study electrically induced release of met-enkephalin. Met enkephalin was measured by high pressure liquid chromatography coupled with radioimmunoassay (RIA) or with RIA alone. We measured the depletion of met enkephalin from guinea pig ileum as a stimulation frequency and duration in normal Krebs and in the presence of protein synthesis inhibitors. Studies are in progress on pre- and post-synaptic control of met-enkephalin release.